Apple Books Merges My Audiobooks

I have a few audiobooks from a series, all of them are .m4b files. When I try to import them into the Apple Books app it just merges them into one super long 100+ hour book. The cover art is for whatever book I import first and plays in the order I import regardless of the true order of the books. How can I import all the books individually so they show up as standalone?

I saw a thread here that is locked suggesting I import into the Music app and manually configure it as an audiobook so it shows in the Books app but I can't seem to get these to import into the Music app (could this be because of the file type)

Any help or suggestions would be greatly appreciated!